1. Field of the Invention
The present invention relates to a thin film magnetic head employed for reproduction of signal magnetization on a magnetic recording medium such as a magnetic tape or the like.
2. Prior Art
The thin film magnetic head (referred to merely as the MR head hereinafter) employing the magnetoresistance effect (referred to merely as MR effect) of a ferromagnetic thin film is suitable for a reproducing head of PCM signals, etc. owing to the facts that its reproducing output does not depend on the relative speed with respect to the recording medium, and that the output thereof is comparatively large. However, for actual use, the thin film magnetic head as described above must be set, in its functioning point, at a place where the linearity thereof is as favorable as possible, since the relation between the external magnetic field and its resistance is non-linear.
Incidentally, in the MR head as described above, shield layers of a high permeability material are disposed at opposite sides of the ferromagnetic thin film for improving a resolution with respect to the signal magnetic field, and therefore, a bias impressing means for effectively applying a bias magnetic field to the ferromagnetic thin film is disposed within the shield layers.
For applying such a bias magnetic field, there has been considered a method for providing a hard magnetic film in the vicinity of the ferromagnetic thin film and a method in which electric current is caused to flow through an electrically conductive film disposed close to the ferromagnetic thin film. However, the former method has a problem related to demagnetization of the recording medium by the hard magnetic film used for the biasing. Meanwhile, the latter practice has such a disadvantage that in the case of a narrow gap head, distortion tends to be large, since the bias current cannot be caused to flow up to the optimum point due to a limitation in the current capacity of the film, and if a push-pull construction is employed for reduction of the distortion, azimuth accuracy of a very high degree is required, thus presenting a difficulty for actual applications from the viewpoint of interchangeability. Moreover, when the bias means as described earlier is disposed in the gap between the ferromagnetic film and the shield layers, this presents an obstruction in the case where the gap length is shortened, and thus, production of the MR head as a short wavelength reproducing head is made difficult.